Briefing following the fatal collision at A421 Bletchley Road and Padbury Road, 4th November 2016.
Collision analysis
Transport for Buckinghamshire (TfB) receives reports from Thames Valley Police on all reported injury collisions that occur on the public highway. In order to identify sites for potential casualty reduction remedial measures,TfB review the number of injury collisions which have occurred within the last 5 year period, in order to identify those sites and routes that have the highest collision rate and casualty severity. A search for collision cluster sites that have a history of 5 or more collisions (of any severity) within a 50m radius within the last 5 years is undertaken. These sites are ranked using a prioritisation system of weighting casualties on a 3, 3, 1 scoring basis, for fatal, serious and slight, to ensure that we are addressing the sites with the highest level of killed or seriously injured casualties (KSIs). When looking at our routes, we rank all A, B and C classified roads based on how many collisions resulting in Killed or seriously injured casualties have occurred per kilometre (KSIs per km).
For context, for the 213 routes assessed and165 cluster sites identified as having a high collision rate, TfB have an annual capital budgetallocated from Public Health funds, of £250,000. This means that this financial year TfB have the budget to carry out some sort of remedial work at 9 locations.
We have previously responded to the effect that this junction did not feature on our cluster site analysis of 5 collisions within 50m within the latest 5 years. This was true at the time as there were less than 5 collisions in the previous 5 year period, and there were 160 sites with a higher incidence of collisions which met this criterion. What has changed is that since August last year there have been 4 reported injury collisions at the junction which not only brings it within this criterion and onto our cluster site list but, due to the severity of these collisions, raises its priority against other sites within that list.
Collision data
Some initial analysis of the reported injury collisions has been undertaken to seek to identify any common factors in the collisions such as contributory factors, location, time of day, road condition, weather, driver details. This analysis is for collisions in the latest 5 years data we have (01/08/2011 to 31/07/2016), I have also included the latest fatal collision in the figures.
There have been 7 collisions, 1 fatal, 3 serious and 3 slight injury, resulting in 1 fatality, 3 serious and 11 slight injured casualties (there have been previous fatalities at the junction - in 1999 and 1990).
4 of these collisions occurred in the pm peak between 4pm and 5.30pm, 3 on weekdays, 2 occurred in the morning peak between 8 am and 10 am.
6 occurred in the Autumn between October and December.
1 in the wet, 1 in snow, 5 dry.
2 in the dark (1 also wet), 5 in the light.
Manoeuvres:
I have attached a plan indicating the manoeuvres involved in the collisions over the last 5 years:
The majority are right turning movements, which is not surprising at a minor/major road staggered junction
3 right turns out of Padbury Road across the path of a westbound vehicle on the A421
1 right turn from Thornborough Road across the path of an eastbound vehicle on the A421
1 right turn from the A412 into Padbury road across a westbound vehicle turning right out of Thornborough Road.
1, 5 vehicle, rear shunt into a left turning westbound vehicle into Padbury Road.
1 U turning vehicle in the Padbury Road junction mouth, but exact details are unclear.
The analysis indicates that the main problem is right turning vehicles from the minor roads onto the A421. The frequent contributory factor is ‘failed to look properly’ against the driver turning out, possibly combined with inappropriate speed approaching the junction on the A421, although ‘excessive speed’ is shown in only one collision (this does not include the latest collision as investigation is still ongoing). Being pm peak times with the right turn it is possibly drivers getting impatient whilst waiting for a gap or under pressure from waiting drivers behind to pull out. The driver postcode analysis may reveal where journeys are being made, are they avoiding the A421 around Buckingham at peak hours?
Further Measures for Potential Consideration
Once the outcome of the police investigation into the recent fatal collision is known, TfB will be in a better position to assess the factors and if they are similar to the previous collision factors.
Areview is now being undertaken within the planning for the 2017/18 safety scheme programmeto investigate possible counter measures, which are subject to available funding.Our initial thoughts are that a roundabout is likely to require some land, realignment of the side roads and lighting. It is likely to take some time to design, consult and build. Funding would have to be found as the current total annual safety scheme budget (as mentioned above) would not cover the anticipated cost of such a large scheme. A signing scheme (possibly vehicle activated) with road markings to highlight the junction and improve recognition of the hazard may be more cost effective and could be implemented within next year’s safety scheme programme.
Peter Chapman
Network Safety Team
Transport for Buckinghamshire
22 November 2016
Collision plot / diagram:
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